Windows QPA: Fix override cursor being cleared when crossing window borders

Override cursors can be modified externally when for example crossing
window borders. Add helper function to enforce the cursor again to
QWindowsWindow::applyCursor() which is called for enter events.

Task-number: QTBUG-69637
Change-Id: Ibea4da9f2aac81377002b626daae64b1102f6c2b
Reviewed-by: Andre de la Rocha <andre.rocha@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

3 files changed, 20 insertions, 5 deletions

diff --git a/src/plugins/platforms/windows/qwindowscursor.cpp b/src/plugins/platforms/windows/qwindowscursor.cpp
index e1a5837201..72155a1d1b 100644
--- a/src/plugins/platforms/windows/qwindowscursor.cpp
+++ b/src/plugins/platforms/windows/qwindowscursor.cpp
@@ -549,6 +549,7 @@ CursorHandlePtr QWindowsCursor::standardWindowCursor(Qt::CursorShape shape)
 }
 
 HCURSOR QWindowsCursor::m_overriddenCursor = nullptr;
+HCURSOR QWindowsCursor::m_overrideCursor = nullptr;
 
 /*!
     \brief Return cached pixmap cursor or create new one.
@@ -621,11 +622,20 @@ void QWindowsCursor::changeCursor(QCursor *cursorIn, QWindow *window)
     }
 }
 
+// QTBUG-69637: Override cursors can get reset externally when moving across
+// window borders. Enforce the cursor again (to be called from enter event).
+void QWindowsCursor::enforceOverrideCursor()
+{
+    if (hasOverrideCursor() && m_overrideCursor != GetCursor())
+        SetCursor(m_overrideCursor);
+}
+
 void QWindowsCursor::setOverrideCursor(const QCursor &cursor)
 {
     const CursorHandlePtr wcursor = cursorHandle(cursor);
-    if (wcursor->handle()) {
-        const HCURSOR previousCursor = SetCursor(wcursor->handle());
+    if (const auto overrideCursor = wcursor->handle()) {
+        m_overrideCursor = overrideCursor;
+        const HCURSOR previousCursor = SetCursor(overrideCursor);
         if (m_overriddenCursor == nullptr)
             m_overriddenCursor = previousCursor;
     } else {
@@ -638,7 +648,7 @@ void QWindowsCursor::clearOverrideCursor()
 {
     if (m_overriddenCursor) {
         SetCursor(m_overriddenCursor);
-        m_overriddenCursor = nullptr;
+        m_overriddenCursor = m_overrideCursor = nullptr;
     }
 }
 
diff --git a/src/plugins/platforms/windows/qwindowscursor.h b/src/plugins/platforms/windows/qwindowscursor.h
index 53f185358b..345f47597e 100644
--- a/src/plugins/platforms/windows/qwindowscursor.h
+++ b/src/plugins/platforms/windows/qwindowscursor.h
@@ -107,7 +107,8 @@ public:
     void changeCursor(QCursor * widgetCursor, QWindow * widget) override;
     void setOverrideCursor(const QCursor &cursor) override;
     void clearOverrideCursor() override;
-    bool hasOverrideCursor() const { return m_overriddenCursor != nullptr; }
+    static void enforceOverrideCursor();
+    static bool hasOverrideCursor() { return m_overriddenCursor != nullptr; }
 
     QPoint pos() const override;
     void setPos(const QPoint &pos) override;
@@ -143,6 +144,7 @@ private:
     mutable QPixmap m_ignoreDragCursor;
 
     static HCURSOR m_overriddenCursor;
+    static HCURSOR m_overrideCursor;
 };
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 3909c64c53..aa40d422fb 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -2419,8 +2419,11 @@ static inline bool applyNewCursor(const QWindow *w)
 
 void QWindowsWindow::applyCursor()
 {
-    if (static_cast<const QWindowsCursor *>(screen()->cursor())->hasOverrideCursor())
+    if (QWindowsCursor::hasOverrideCursor()) {
+        if (isTopLevel())
+            QWindowsCursor::enforceOverrideCursor();
         return;
+    }
 #ifndef QT_NO_CURSOR
     if (m_cursor->isNull()) { // Recurse up to parent with non-null cursor. Set default for toplevel.
         if (const QWindow *p = window()->parent()) {